NASA's DART spaceship on Monday struck the asteroid Dimorphos, in a test designed to ascertain whether a similar action could in future be used to deflect an asteroid or a comet that's bound for Earth.
Impact occurred at 7:14 p.m. Eastern Time in the US (2314 GMT/UTC), 10 months after the vessel had launched towards the harmless asteroid.
"We're embarking on a new era, an era in which we potentially have the capability to protect ourselves from something like a dangerous hazardous asteroid impact," said Lori Glaze, director of NASA's planetary science division.
Video footage from the spacecraft and images of NASA's ground control team responding to the direct hit were broadcast live online. The abrupt cancellation of DART's radio feed, coupled with still images of the asteroid's surface from very close range roughly one second before impact, served as evidence of it having hit its target at around 14,000 miles per hour (22,500 km/h).
But did it work?
The experiment is the first of its kind. It will take some time to learn whether the successful impact also meaningfully altered Dimorphos' trajectory.
A tiny satellite called LICIACube separated from DART a few weeks ago. It is supposed to make a close pass of the site to capture images after the collision of what's known as the ejecta, the rock and debris thrown off the asteroid in the impact.
Ground satellites will be able to log whether or not Dimorphos' orbit of another asteroid, Didymos, has been altered by the impact as NASA hopes it will be.
"Now is when the science starts," said NASA's Glaze. "Now we're going to see for real how effective we were."
It could take days or even weeks to chart Dimorphos' new trajectory.
The mission, which cost $325 million (roughly €340 million), is the first attempt to shift the position of any object in space simply using the kinetic energy of an impact.
Dress rehearsal for a real Earth deflection
There are currently no known asteroids, comets or other "near-Earth objects" (NEOs), to use NASA's terminology, that are on a collision course with Earth. However, scientists warn that a significant number of such objects are likely yet to be discovered.
There would appear to be few alternatives available should such a rock be Earth-bound, with deflecting its course just enough to make it miss the planet being the most likely means of defense, and one already explored by Hollywood in films like "Armageddon."
The alternative, trying to blow up a large space rock, runs the risk of turning one large impact into hundreds or thousands of smaller ones — by shattering the NEO and having the fragments rain down on the planet instead.
One step ahead of the dinosaurs
"The dinosaurs didn't have a space program to help them know what was coming, but we do," NASA's senior climate advisor Katherine Calvin said, referring to the mass extinction more than 60 million years ago believed to have been caused, or at least partially caused, by a major asteroid impact in Mexico's Yucatan Peninsula.